1. Field of the Invention
The present invention relates to an automatic document feeder designed to automatically feed a document toward a document read surface so as to read an image of the document, and an image forming apparatus equipped with the automatic document feeder.
2. Description of the Related Art
Heretofore, there has been known an automatic document feeder as disclosed in Japanese Patent Laid-Open Publication No. 2003-87510. This automatic document feeder is adapted to be used with an image forming apparatus, such as a copy machine or a facsimile machine, which is designed to read an image from a document. The automatic document feeder comprises a housing adapted to openably/closably cover a platen (contact glass) disposed on a top surface of a body of the image forming apparatus, a document tray attached to an upper portion of the housing and adapted to place thereon a stack of documents, a document feeding mechanism adapted to feed the documents one-by-one from the document tray and lead the document onto the contact glass, and a catch tray adapted to receive the document after being fed on the contact glass by the document feeding mechanism and then subjected to an optical reading operation of reading an image thereon using an optical system unit. The catch tray is disposed in the housing at a position below and opposed to the document tray.
The housing is provided with a restriction member adapted to press the document being passing above the contact glass, against the contact glass, so as to restrict floating of the document. Further, a Mylar sheet is attached to a bottom surface of the restriction member. A leading member and a guide plate are disposed on a downstream side of the contact glass in this order in such a manner as to form an inclined surface which extends upwardly in a downstream direction to lead the document to the catch tray therealong. The Mylar sheet is disposed to extend up to a top surface of the guide plate.
Thus, after passing above the contact glass while being sandwiched between the contact glass and the restriction member through the Mylar sheet, the document passes between the leading member and the Mylar sheet, and then travels between the Mylar sheet and the guide plate while being sandwiched therebetween. Finally, the document is ejected into the catch tray. The guide plate is positioned to have an upstream end located below a downstream end of the inclined surface of the leading member, so that the document after passing above the leading member is reliably guided to the top surface of the guide plate.
In the Japanese Patent Laid-Open Publication No. 2003-87510, it is described that the Mylar sheet arranged on the bottom surface of the restriction member makes it possible to stabilize a document carrying speed by preventing occurrence of a problem that the document flutters on the contact glass, so as to provide a stable carrying state of the document to avoid warping or distortion in a read image.
Generally, a housing adapted to openably/closably cover a contact glass is mounted to an apparatus body in such a manner as to be swingably moved in open and closed directions about a hinge plate. The hinge plate is typically provided with bias means, such as a plate spring, to facilitate an open movement of the housing, so that the housing is biased in the open direction by a biasing force of the bias means. In reality, fluctuation in the biasing force of the bias means or pinching of foreign matters is likely to cause variations in surface contact of the housing with the contact glass.
Reviewing the automatic document feeder disclosed in Japanese Patent Laid-Open Publication No. 2003-87510 from the above standpoint, the guide plate for leading the document is fixed to the housing, and thereby it is unable to cope with the variations in surface contact of the housing with the contact glass. Thus, if the housing is located opposed to the contact glass to slightly lift the guide plate, the document is likely to collide with an upstream edge of the guide plate. In the worst case, the document gets into a gap between the guide plate and the contact glass to cause a problem of precluding the document from being adequately carried.
Conversely, if the housing is slightly lowered relative to its normal position, the guide plate is likely to collide with the top surface of the apparatus body when the housing is fully closed, to cause a problem about damages in the guide plate or the top surface of the apparatus body.